Heat Exchanger for an Oil Storage Tank

ABSTRACT

A heating assembly for heating a liquid storage tank includes a heat exchanger tank supported in one wall of the storage tank to extend into the storage tank in contact with liquid stored therein. The heat exchanger tank contains a heat exchanger fluid therein which is heated by a heating apparatus extending through the heat exchanger tank whereby heat is only transferred to the liquid in the storage tank through the heat exchanger fluid. The heating apparatus extending through the heat exchanger tank may be a burner tube or an electrical resistance-type heating element according to different embodiments of the invention.

This application is a continuation-in-part of US parent application Ser.No. 14/178,919, filed Feb. 12, 2014, and claims the benefit under 35U.S.C.119(e) of U.S. provisional application Ser. No. 61/763,603, filedFeb. 12, 2013.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger arranged to bereceived in a storage tank, for example an oil storage tank, in whichthe each exchanger contains a heat exchanger fluid therein and receivesa heating apparatus extending therethrough for heating the contents inthe storage tank by communicating heat from the heating apparatusthrough the heat exchanger fluid. The heating apparatus may comprise aburner tube of a propane burner or an electrical resistance-type heatingelement. More particularly, the present invention relates to a heatexchanger for a heating apparatus in an oil storage tank which furtherincludes a production passage extending through the heat exchanger fluidin the heat exchanger tank for heating produced hydrocarbons as they aredirected through the production passage into the oil storage tank.

BACKGROUND

In oil production, it is common to locate an oil storage tank at an oilwell site to produce hydrocarbons from the well directly into the oilstorage tank. It is also known to provide a propane burner which directsexhaust into a burner tube extending into the oil storage tank forheating oil in the tank. Heating the oil assist in settling sand out ofthe oil to the bottom of the tank and assists with fluidity of the oilwhen subsequently pumping the oil into transport tanker trucks.

Occasionally oil is pumped from the oil storage tank into tanker truckssuch that the level of oil in the storage tank falls below the elevationof the burner tube in the storage tank. The burner tube in this instancecan become excessively hot such that there is danger of ignitingvolatile hydrocarbons in gaseous form surrounding the burner tube.Ignition of the fumes can cause explosions which damage the tank and area safety concerns for operators of the storage tank or tanker trucks.

U.S. Pat. No. 7,726,298 by St. Denis discloses a method and apparatusfor heating a liquid storage tank in place of a conventional burnertube. An engine is disposed in an engine compartment appended to aperipheral sidewall of the tank and an exhaust conduit extends into theinterior of the liquid storage tank from the engine such that heat fromhot exhaust gases passing through the exhaust conduit heats the interiorof the liquid storage tank. The exhaust conduit can still becomeexcessively hot and is in direct contact with volatile hydrocarbons inthe storage tank such that the same risk of ignition and explosions asnoted above remains present.

U.S. Pat. No. 7,293,606 by Benoit discloses a heat exchanging apparatusincluding a gas fuelled flameless catalytic heater. According to oneembodiment, an oil storage tank is heated by locating the catalyticheater remotely from the tank and communicating heat exchanger fluid ina loop between the catalytic heater and a heater coil in the tank.Although the risk of combustion within the oil storage tank may bereduced as compared to use of a burner tube, the heater coil can bedifficult to maintain as it is subjected to abrasive sands and corrosivefluids within the oil storage tank.

Electrical resistant heater coils have been used by immersion withinvarious prior art fluid tanks, such as residential hot water tanks;however, when used within a hydrocarbon storage tank for heating the oiltherein, the heater coil is subjected to abrasive sands and corrosivefluids within the oil storage tank. Variation the diameter of the coilcan produce dangerous hot spots. Also, the heat transfer through thecontents within a hydrocarbon storage tank typically relies onconduction through the hydrocarbons as the heavy fluid involves minimalfluid movement, particularly when there is an abundance of sludge andsand therein, such that the very small heat transfer area of the heatercoil is very inefficient at evenly distributing heat throughout thestorage tank.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a heatingassembly for heating a liquid storage tank having walls surrounding ahollow interior arranged to contain a liquid therein, the assemblycomprising:

a heat exchanger tank including boundary walls containing a heatexchanger fluid therein;

a heating apparatus supported within the heat exchanger tank;

the heat exchanger tank being arranged to be supported within the liquidstorage tank such that heat from the heating apparatus is arranged to becommunicated through the heat exchanger fluid and the boundary walls ofthe heat exchanger tank directly to liquid in the liquid storage tank.

The heating apparatus may comprises a burner tube extending through theheat exchanger tank and being arranged to be coupled to an externalburner so as to direct exhaust from the burner therethrough, or anelectrical resistance-type heating element extending through the heatexchanger tank.

The heat exchanger fluid surrounding the heating apparatus maintainsfluid contact with the heating apparatus to prevent the heatingapparatus from reaching excessive temperature which could otherwise riskigniting vapours in the oil storage tank. The heat exchanger tank alsolimits direct contact of the heating apparatus with hydrocarbons in thestorage tank to further minimize the risk of igniting hydrocarbons inthe oil storage tank.

The heat exchanger tank received within the oil storage compartment ofthe oil storage tank allows heat to be transferred directly from theheat exchanger fluid, through the boundary walls of the heat exchangertank, directly to the surrounding oil in the storage tank. The heatexchanger tank occupies a much larger volume than the heating elementalone for more even transfer of heat to the surrounding oil in thestorage tank. Furthermore, the heat exchange tank fully surrounds theheating element such that the heating element is fully protected fromabrasive sands and corrosive fluids within the storage tank.

Preferably the heat exchanger tank is arranged to be supported withinthe oil storage tank such that heat is only communicated from theheating apparatus to the liquid in the storage tank through the heatexchanger fluid.

Preferably the heat exchanger tank is arranged to be supported insealing engagement with one of the walls of the oil storage tank.

Preferably the heat exchanger tank is arranged to extend generallyhorizontally inward from an upright boundary wall of the storage tank.

The heat exchanger tank may be used in combination with a productiontank arranged to receive produced hydrocarbons therein directly from awell.

Preferably the heat exchanger tank further comprises an overflow tanklocated externally of the heat exchanger tank and an overflow passage incommunication between the overflow tank and the heat exchanger tank soas to be arranged to permit expansion of the heat exchanger fluid fromthe heat exchanger tank into the overflow tank.

Preferably a fluid level monitor is arranged to monitor a level of heatexchanger fluid in the heat exchanger tank. In this instance thecontroller may be arranged to cease operation of the heating apparatusresponsive to a level of the heat exchanger fluid as monitored by thefluid level monitor falling below a prescribed lower level limit.

Preferably a heat exchanger temperature monitor is arranged to monitor atemperature of the heat exchanger fluid in the heat exchanger tank. Inthis instance the controller may be arranged to cease operation of theheating apparatus responsive to a temperature of the heat exchangerfluid as monitored by the heat exchanger temperature monitor exceeding aprescribed upper temperature limit.

Preferably a heat exchanger temperature monitor is arranged to monitor atemperature of the heat exchanger fluid in the heat exchanger tank. Inthis instance the controller may be arranged to actuate operation of theheating apparatus responsive to a temperature of the heat exchangerfluid as monitored by the heat exchanger temperature monitor fallingbelow a prescribed lower temperature limit.

Preferably a storage temperature monitor is arranged to monitor atemperature of the liquid in the liquid storage tank. In this instancethe controller may be arranged to cease operation of the heatingapparatus responsive to a temperature of the liquid as monitored by thestorage temperature monitor exceeding a prescribed upper temperaturelimit.

Preferably the heat exchanger tank includes a perimeter flangeprojecting outwardly from the boundary walls about a circumference ofthe heat exchanger tank in which the perimeter flange is arranged to bemounted in sealing engagement about a perimeter of an opening in thewall of the oil storage tank.

Preferably the perimeter flange is defined by a perimeter edge of an endwall at one end of the heat exchanger tank.

Preferably the perimeter flange includes spaced apart mounting aperturesformed therein so as to be arranged to secure the flange to theperimeter of the opening in the wall of the oil storage tank usingthreaded fasteners.

Preferably the heat exchanger fluid comprises heat transfer oil.

Preferably a production passage communicates through the heat exchangertank between an inlet end of the production passage arranged to receiveproduced fluid from a well therein and outlet of the production passagearranged for communication with the hollow interior of the storage tanksuch that the production passage is in heat exchanging relationship withthe heating apparatus through the heat exchanger fluid.

Preferably the production passage follows a sinuous path through theheat exchanger tank.

Preferably the production passage is above the heating assembly.

According to a further aspect of the present invention there is providedmethod of producing hydrocarbons from a well comprising a wellhead, themethod comprising:

providing a storage tank in proximity to the well having an interiorstorage chamber for storing produced hydrocarbons therein;

providing a heating assembly comprising:

-   -   a heat exchanger tank received within the interior of the        storage chamber of the storage tank, the heat exchanger tank        including boundary walls containing a heat exchanger fluid        therein; and    -   a heating apparatus supported within the heat exchanger tank;

directing produced hydrocarbons from the well into the interior storagechamber of the storage tank; and

heating the produced hydrocarbons in the interior storage chamber of thestorage tank by actuating the heating apparatus such that heat from theheating apparatus is arranged to be communicated through the heatexchanger fluid and the boundary walls of the heat exchanger tankdirectly to the produced hydrocarbons in the storage tank.

Various embodiments of the invention will now be described inconjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of the heatingassembly;

FIG. 2 is a sectional view of the heating assembly according to thefirst embodiment along the line 2-2 in FIG. 1.

FIG. 3 is a perspective view of the heating assembly according to thefirst embodiment of FIG. 1, shown supported on a horizontal tank;

FIG. 4 is a perspective view of the heating assembly according to thefirst embodiment of FIG. 1, shown supported on an upright tank;

FIG. 5 is a schematic representation of a sectional view along the line2-2 in FIG. 1 according to a second embodiment;

FIG. 6 is a perspective view of a third embodiment of the heatingassembly; and

FIG. 7 is a sectional view of the heating assembly according to thethird embodiment along the line 7-7 in FIG. 6.

In the drawings like characters of reference indicate correspondingparts in the different figures.

DETAILED DESCRIPTION

Referring to the accompanying figures, there is illustrated a heatingassembly generally indicated by reference numeral 10. The assembly 10 issuited for heating a liquid storage tank 12 having tank boundary walls14 surrounding the hollow interior which defines a main liquid storageportion for storing liquid, for example oil therein.

According to the first and second embodiments of FIGS. 1 through 5, theheating assembly 10 is used with a burner head 16, for example a propaneburner and is mounted within the oil storage tank in place of aconventional burner tube extending into the tank for heating the oiltherein.

According to the third embodiment of FIGS. 6 and 7, the heating assembly10 is used with an electrical resistance-type heating apparatus 15, andis mounted within the oil storage tank instead of a conventionalelectric heater coil. Contrary to the present invention, a conventionalelectric heater coil would be mounted to extend directly into the oilstorage tank in direct communication with the oil in the storage tankfor heating the oil therein.

Although various embodiments are shown in the accompanying figures, thecommon features of the first and second embodiments will first bedescribed.

The assembly 10 is mounted into a suitable opening 18 formed in anupright one of the walls 14 of the tank. A heat exchanger tank 20 of theassembly extends into the storage tank through the opening 18 so as tobe elongate and extend generally horizontally inward into the tank froma first end 22 at the wall of the tank to an inner second end 24. Thetank 20 is fully closed on all sides by respective side walls 26 andenclosed at both of the first and second ends by respective ends walls28 such that the interior of the heat exchanger tank is a fixed closedvolume containing a heat exchanger fluid therein which fills the tank.

At the first end of the tank 20, the end wall 28 comprises a generallyvertically oriented end plate which protrudes beyond the side wallsabout the full perimeter edge thereof to define a perimeter flange 30extending about a full circumference of the heat exchanger tank at thefirst end thereof. The perimeter flange overlaps the side wall of theoil storage tank within which the heat exchanger tank is mounted aboutthe full perimeter of the opening 18. Mounting apertures 32 are locatedat circumferentially spaced positions about the perimeter flange so asto permit mounting to the tank wall about the perimeter of the openingusing suitable threaded fasteners for example. A gasket 34 may beprovided about the perimeter of the opening 18 of the tank wall to beclamped between the storage tank and the perimeter mounting flange ofthe heat exchanger tank so that the heat exchanger tank is mounted insealing engagement with the storage tank wall about the full perimeterthereof.

The assembly further includes a burner tube 36 which is generallyU-shaped so as to comprise two elongate sections 38 extendinghorizontally and longitudinally substantially between the first andsecond ends of the heat exchanger tank. The two sections 38 are joinedat the second end of the tank by a curved section to define the U-shapeof the burner tube.

A lowermost one of the two sections 38 protrudes through the end wall 28at the first end of the tank to define an inlet of an exhaust passagedefined by the burner tube. A suitable bolt flange 40 about the inletpermits coupling to a burner head 16 for receiving the products ofcombustion therefrom in use to heat the burner tube and thus heat theoil in the storage tank as described in further detail below.

The uppermost section 38 of the burner tube similarly protrudes throughthe end wall 28 at the first end of the heat exchanger tank above theinlet. The portion of the second section protruding to the exterior iscoupled to a vertical stack 42 to define an outlet of the exhaustpassage defined by the burner tube which is vented to atmosphere.

The main portion of the burner tube between the inlet and outlet endsthereof as defined primarily by the first and second sections 38 and thecurved section therebetween is fully contained within the heat exchangertank. The heat exchanger tank is in turn mounted within the storage tankwall so that the main portion of the burner tube is the only portionreceived within the storage tank and also such that the main portion isfully surrounded by heat exchanger fluid contained within the heatexchanger tank. In a preferred embodiment, the heat exchanger fluid is aheat transfer oil. Regardless of the type of heat exchanger fluid, theheat exchanger tank is mounted such that heat can only be communicatedfrom the burner tube to the oil in the main oil storage portion of thestorage tank through the heat exchanger fluid in the heat exchangertank. This ensures no direct communication between the burner tube andthe oil in the storage tank.

In use, the heating assembly is installed in a storage tank by providinga suitable opening in the upright wall of the tank so that the heatexchanger tank can be substantially fully inserted into the oil storagetank to extend longitudinally and horizontally inward from the first endof the tank wall to the second end terminating internally within the oilstorage tank. Using the gasket and bolts through the perimeter mountingflange the first end of the heat exchanger tank is mounted in sealingengagement about the perimeter of the opening in the storage tank wall.

The burner head is coupled to the inlet of the burner tube and operatedsuch that the products of combustion from the burner head are directedthrough the burner tube from the inlet to the outlet to heat up theburner tube and in turn heat up the heat exchanger fluid surrounding theburner tube. The heat transferred to the fluid is in turn transferred tothe oil through the increased exterior surface area of the heatexchanger tank.

As shown in FIG. 3, when the tank includes a cylindrical wall extendinghorizontally between two opposing end walls, the heat exchanger tank istypically mounted in one of the upright end walls.

Alternatively, as shown in FIG. 4, when the storage tank comprises anupright cylindrical side wall, typically the heat exchanger tank ismounted in an opening in the cylindrical wall.

Turning now more particularly to the first embodiment of FIGS. 1 through4, the assembly 10 in this instance further includes a productionpassage 44 in the form of an elongate pipe extending through the heatexchanger tank to be surrounded by heat exchanger fluid therein. Theproduction passage extends from a first end protruding through the endwall 28 at the first end of the heat exchanger tank at a location belowthe burner tube to a second end which is open to the hollow interior ofthe main oil storage portion of the storage tank. Although the passage44 is shown below in FIGS. 1 through 5, in preferred embodiments, thepassage 44 is located above the burner tube.

The first end of the production passage includes the bolt flange 46 atthe exterior of the heat exchanger tank to permit coupling to suitableoil production equipment to receive produced oil directly therein, thusdefining an inlet 48 of the production passage. Produced fluids arecommunicated from the inlet towards an opposing outlet 50 defined by thesecond end of the production passage at the second end of the heatexchanger tank.

The production passage is comprised of plural lengths of pipe joined bycurved sections to define a sinuous path from the inlet to the outletthrough the heat exchanger fluid. The winding and non-linear path of theproduction passage increases the duration that the produced fluids arein heat exchanging relationship with the heat exchanger fluid.

Connecting oil production equipment to the inlet of the productionpassage also allows heat to be transferred from the burner tube to theproduced fluids in the production passage 44 by transferring heat acrossthe heat exchanger fluid in the heat exchanger tank surrounding both theburner tube and the production passage.

Turning now more particularly to the embodiment of FIG. 5, the structureof the heat exchanger tank is substantially identical to the embodimentof FIGS. 1 through 4; however, additional controls are provided. Infurther embodiments, the additional controls may also be used incombination with the production passage 44.

As shown in FIG. 5, a controller 60 is provided which controls operationof the burner head 16. The controller 60 works in cooperation withvarious sensors as described herein. One of the sensors is a heatexchanger temperature monitor 64 mounted on the outer end wall 28 of theheat exchanger tank 20 at an intermediate height between the burner headand the exhaust portion of the burner tube. The heat exchangertemperature monitor 64 is arranged to monitor a temperature of the heatexchanger fluid in the heat exchanger tank. The monitored temperature isrelayed to the controller with all other monitored data. In thisinstance, the controller 60 is arranged to both: i) actuate operation ofthe burner head responsive to a temperature of the heat exchanger fluidas monitored by the heat exchanger temperature monitor falling below aprescribed lower temperature limit, and ii) cease operation of theburner head responsive to a temperature of the heat exchanger fluid asmonitored by the heat exchanger temperature monitor exceeding aprescribed upper temperature limit. The heat exchanger is thusmaintained substantially between the upper and lower temperature limits.

A storage temperature monitor 66 is also provided for monitoring atemperature of the liquid in the liquid storage tank. The storagetemperature monitor 66 is supported in the boundary wall of the storagetank, spaced apart laterally from the heat exchanger tank, at anelevation which is near a vertical center of the storage tank and theheat exchanger tank respectively. The storage temperature monitorcommunicates through the boundary wall of the storage tank so as to bein contact with the liquid stored in the storage tank 12. The controller60 in this instance is arranged to cease operation of the burner headresponsive to a temperature of the liquid as monitored by the storagetemperature monitor exceeding a prescribed upper temperature limitregardless of the condition sensed by the heat exchanger temperaturemonitor. More particularly, if the liquid temperature in the storagetank exceeds the respective upper storage temperature limit, the burnerhead is not operated even if the heat exchanger temperature monitorindicates a temperature below the upper limit thereof.

Another one of the sensors associated with the controller is a fluidlevel monitor 62 which is supported on the outer end wall 28 of the heatexchanger tank 20 to communicate through the end wall with fluid insidethe tank. More particularly, the fluid level monitor 62 is arranged tomonitor a level of heat exchanger fluid in the heat exchanger tank bydetermining if the fluid is in contact with the monitor or not. Themonitor is mounted above the height of the burner tubes to define aminimum operational height of the liquid. The controller 60 monitors iffluid is in contact with the monitor 62 to determine if the height ofthe fluid is above or below the level of the monitor 62. Accordingly thecontroller can be arranged to cease operation of the burner head 16responsive to a level of the heat exchanger fluid falling below aprescribed lower level limit defined by the location of the monitor asindicated by a lack of fluid contact with the monitor 62. The operationof the burner head is prevented in the instance of a fluid level belowthe fluid level monitor 62 even if the temperature monitors indicate aheating demand.

Also shown in FIG. 5, an overflow tank 68 is supported externally of thestorage tank 12 and the heat exchanger tank 20 by being supported alongan exterior of the outer end wall 28 of the heat exchanger tank andalong an exterior of one of the boundary walls of the storage tank 12.The overflow tank 68 locates a surplus of the heat exchanger fluidtherein. The overflow tank 68 is elongate in a vertical direction and issupported such that a majority of the tank extends upwardly above thetop end of the heat exchanger tank 20. An overflow passage 70 in theform of a small diameter tube or pipe is in open fluid communicationbetween a bottom end of the overflow tank and a top end of the heatexchanger tank so as to be arranged to permit expansion of the heatexchanger fluid from the heat exchanger tank into the overflow tank andso as to ensure the heat exchanger tank remains always full in itsentirety with heat exchanger fluid. The top end of the overflow tankincludes a vent 72 which is vented to atmospheric pressure.

FIG. 5 further illustrates a drain fitting 74 in communication throughthe outer end wall 28 of the heat exchanger tank 20 adjacent the bottomend thereof. The drain fitting 74 can be capped or provided with a valveto maintain the fitting in a closed state under normal operation. Thedrain fitting is typically only opened when it is desired to drain theheat exchanger fluid from the heat exchanger tank, for example whenperforming maintenance on the assembly.

A thermometer 76 can also be mounted externally on the outer end wall 28of the heat exchanger tank to display temperature of the fluid withinthe heat exchanger tank as measured by the thermometer in communicationwith the fluid.

The assembly according to FIG. 5 is operated in the manner describedabove to heat contents of the storage tank for treatment and the like.In a preferred embodiment, the storage tank receives producedhydrocarbons therein which may be heated for example to assist in thesettling of sand from the oil. The controller 60 receives data from thevarious monitors described above and operates the burner head tomaintain the heat exchanger fluid between upper and lower limits, whilesimultaneously ensuring that the temperature of the contents of thestorage tank remain between upper and lower limits. For added safety,the burner is prevented from operating if the fluid level in the heatexchanger tank falls below a prescribed limit.

Turning now to the third embodiment of FIGS. 6 and 7, the assembly 10 isagain mounted into a storage tank opening 18 formed in an upright one ofthe walls 14 of the tank. The tank in this instance includes a collar 19which is joined to the perimeter edge of the wall 14 of the tank aboutthe tank opening 18, to project perpendicularly outward from the wallconcentrically with the tank opening 18. A mounting flange 21 extendsradially outwardly from the collar 19, about the full perimeter of thetank opening 18. The mounting flange lies parallel to and spacedoutwardly from the tank wall 14 such that the assembly 10 may be readilyfastened thereto as described in further detail below.

A heat exchanger tank 20 of the assembly extends into the storage tankthrough the opening 18 so as to be elongate in a longitudinal directionextending generally horizontally inward into the tank from a first end22 at the wall of the tank to an inner second end 24. The tank 20 isfully closed on all sides by respective side walls 26 and enclosed atboth of the first and second ends by respective ends walls 28 such thatthe interior of the heat exchanger tank is a fixed volume containing aheat exchanger fluid therein, for example a heat transfer oil or glycol,which fills the tank.

At the first end of the tank 20, the end wall 28 comprises a generallyvertically oriented end plate which protrudes beyond the side wallsabout the full perimeter edge thereof to define a perimeter flange 30extending about a full circumference of the heat exchanger tank at thefirst end thereof. The perimeter flange overlaps the mounting flange 21about the tank opening 18 within which the heat exchanger tank isreceived. Co-operating mounting apertures 32 in the mounting flange 21of the storage tank and the perimeter flange 30 of the heating assemblypermit fasteners to secure the flanges together about the full perimeterof the opening 18 using suitable threaded fasteners for example. Anannular gasket 34 may be provided between the flanges prior to fasteningso that the gasket is received about the full circumference of theopening 18, clamped between the storage tank and the perimeter mountingflange of the heat exchanger tank. Accordingly, the heat exchanger tankis mounted in sealing engagement with the storage tank wall about thefull perimeter thereof.

The heating apparatus 15 includes a resistance type heating element 37which is submerged within the heat exchanger fluid in the heat exchangertank, and a controller 61 which regulates electrical power delivered tothe heating element 37 to produce heat. The heating element includes aplurality of winding sections 39 which follow a sinuous pathsubstantially evenly distributed throughout the volume of the heatexchanger tank to provide substantially uniform heat to the heatexchanger fluid within the heat exchanger tank. A sealed port 41communicates the heat element 37 through the exterior end wall 28 insealing engagement with the end wall to prevent the escape of heatexchanger fluid therethrough.

The heating element is fully received and contained within the heatexchanger tank, and in turn, the heat exchanger tank is mounted withinthe storage tank wall so that the heat exchanger tank is substantiallyfully received within the interior storage volume of the oil storagetank. Although in the preferred embodiment the heat exchanger fluid is aheat transfer oil, regardless of the type of heat exchanger fluid, theheat exchanger tank is mounted such that heat can only be communicatedfrom the heating element to the oil in the main oil storage portion ofthe storage tank through the heat exchanger fluid in the heat exchangertank. This ensures no direct communication between the heating elementand the oil in the storage tank.

The heating assembly 10 optionally further includes a production passage44 in the form of an elongate pipe extending through the heat exchangertank to be surrounded by heat exchanger fluid therein. The productionpassage extends from a first end protruding through the end wall 28 atthe first end of the heat exchanger tank at a location above the heatingelement to a second end which is open to the hollow interior of the mainoil storage portion of the storage tank.

The first end of the production passage includes the bolt flange 46 atthe exterior of the heat exchanger tank to permit coupling to suitableoil production equipment to receive produced oil directly therein, thusdefining an inlet 48 of the production passage. Produced fluids arecommunicated from the inlet towards an opposing outlet 50 defined by thesecond end of the production passage at the second end of the heatexchanger tank.

The production passage is comprised of plural lengths of pipe joined bycurved sections to define a sinuous path from the inlet to the outletthrough the heat exchanger fluid. The winding and non-linear path of theproduction passage increases the duration that the produced fluids arein heat exchanging relationship with the heat exchanger fluid.

Connecting oil production equipment to the inlet of the productionpassage also allows heat to be transferred upwardly from the heatingelement to the produced fluids in the production passage 44 bytransferring heat across the heat exchanger fluid in the heat exchangertank surrounding both the heating element and the production passage.

With regard to operation of the heating element, the controller 61 worksin cooperation with various sensors as described herein. One of thesensors is a heat exchanger temperature monitor 64 mounted on the outerend wall 28 of the heat exchanger tank 20 at an intermediate heightwhich is centrally located between the top and bottom ends of the heatexchanger tank. The heat exchanger temperature monitor 64 is arranged tomonitor a temperature of the heat exchanger fluid in the heat exchangertank. The monitored temperature is relayed to the controller with allother monitored data.

In this instance, the controller 61 is arranged to both: i) actuateoperation of the electric heating element responsive to a temperature ofthe heat exchanger fluid as monitored by the heat exchanger temperaturemonitor falling below a prescribed lower temperature limit, and ii)cease operation of the electric heating element responsive to atemperature of the heat exchanger fluid as monitored by the heatexchanger temperature monitor exceeding a prescribed upper temperaturelimit. The heat exchanger is thus maintained substantially between theupper and lower temperature limits.

A storage temperature monitor 66 is also provided for monitoring atemperature of the liquid in the liquid storage tank. The storagetemperature monitor 66 is supported in the boundary wall of the storagetank, spaced apart laterally from the heat exchanger tank, at anelevation which is near a vertical center of the storage tank and theheat exchanger tank respectively. The storage temperature monitorcommunicates through the boundary wall of the storage tank so as to bein contact with the liquid stored in the storage tank 12.

The controller 61 in this instance is arranged to cease operation of theelectric heating element responsive to a temperature of the liquid asmonitored by the storage temperature monitor exceeding a prescribedupper temperature limit regardless of the condition sensed by the heatexchanger temperature monitor. More particularly, if the liquidtemperature in the storage tank exceeds the respective upper storagetemperature limit, the electric heating element is not operated even ifthe heat exchanger temperature monitor indicates a temperature below theupper limit thereof.

Another one of the sensors associated with the controller is a fluidlevel monitor 62 which is supported on the outer end wall 28 of the heatexchanger tank 20 to communicate through the end wall with fluid insidethe tank. More particularly, the fluid level monitor 62 is arranged tomonitor a level of heat exchanger fluid in the heat exchanger tank bydetermining if the fluid is in contact with the monitor or not. Themonitor is mounted above the height of an uppermost portion of theheating element to define a minimum operational height of the liquid.

The controller 61 monitors if fluid is in contact with the monitor 62 todetermine if the height of the fluid is above or below the level of themonitor 62. Accordingly the controller can be arranged to ceaseoperation of the electrical heating element responsive to a level of theheat exchanger fluid falling below a prescribed lower level limitdefined by the location of the monitor as indicated by a lack of fluidcontact with the monitor 62. The operation of the electric heatingelement is prevented in the instance of a fluid level below the fluidlevel monitor 62 even if the temperature monitors indicate a heatingdemand.

The heating assembly also includes an overflow tank 68 which issupported externally of the storage tank 12 and the heat exchanger tank20 by being supported along an exterior of the outer end wall 28 of theheat exchanger tank and along an exterior of one of the boundary wallsof the storage tank 12. The overflow tank 68 locates a surplus of theheat exchanger fluid therein. The overflow tank 68 is elongate in avertical direction and is supported such that a majority of the tankextends upwardly above the top end of the heat exchanger tank 20. Anoverflow passage 70 in the form of a small diameter tube or pipe is inopen fluid communication between a bottom end of the overflow tank and atop end of the heat exchanger tank so as to be arranged to permitexpansion of the heat exchanger fluid from the heat exchanger tank intothe overflow tank and so as to ensure the heat exchanger tank remainsalways full in its entirety with heat exchanger fluid. The top end ofthe overflow tank includes a vent 72 which is vented to atmosphericpressure.

A drain fitting 74 is also provided in communication through the outerend wall 28 of the heat exchanger tank 20 adjacent the bottom endthereof. The drain fitting 74 can be capped or provided with a valve tomaintain the fitting in a closed state under normal operation. The drainfitting is typically only opened when it is desired to drain the heatexchanger fluid from the heat exchanger tank, for example whenperforming maintenance on the assembly.

A thermometer 76 can also be mounted externally on the outer end wall 28of the heat exchanger tank to display temperature of the fluid withinthe heat exchanger tank as measured by the thermometer in communicationwith the fluid.

In use, the heating assembly is installed in a storage tank by providinga suitable opening 18 in the upright wall of the tank with acorresponding mounting flange about the opening so that the heatexchanger tank can be substantially fully inserted into the oil storagetank to extend longitudinally and horizontally inward from the first endof the tank wall to the second end terminating internally within the oilstorage tank. Using the gasket and bolts through the perimeter mountingflange the first end of the heat exchanger tank is mounted in sealingengagement about the perimeter of the opening in the storage tank wall.

As shown in FIG. 3, when the tank includes a cylindrical wall extendinghorizontally between two opposing end walls, the heat exchanger tank istypically mounted in one of the upright end walls.

Alternatively, as shown in FIG. 4, when the storage tank comprises anupright cylindrical side wall, typically the heat exchanger tank ismounted in an opening in the cylindrical wall.

The heating assembly 10 is operated as described above to heat contentsof the storage tank for treatment and the like. In a preferredembodiment, the storage tank receives produced hydrocarbons therein,which may be heated, for example to assist in the settling of sand fromthe oil. The controller 61 receives data from the various monitorsdescribed above and operates the electrical heating element to maintaintemperature of the heat exchanger fluid between upper and lower limits,while simultaneously ensuring that the temperature of the contents ofthe storage tank remains between upper and lower limits. For addedsafety, the heating element is prevented from operating if the fluidlevel in the heat exchanger tank falls below a prescribed limit.

Since various modifications can be made in my invention as herein abovedescribed, and many apparently widely different embodiments of same madewithin the spirit and scope of the claims without department from suchspirit and scope, it is intended that all matter contained in theaccompanying specification shall be interpreted as illustrative only andnot in a limiting sense.

1. A heating assembly for heating a liquid storage tank having wallssurrounding a hollow interior arranged to contain a liquid therein, theassembly comprising: a heat exchanger tank including boundary wallscontaining a heat exchanger fluid therein; a heating apparatus supportedwithin the heat exchanger tank; the heat exchanger tank being arrangedto be supported within the liquid storage tank such that heat from theheating apparatus is arranged to be communicated through the heatexchanger fluid and the boundary walls of the heat exchanger tankdirectly to liquid in the liquid storage tank.
 2. The assembly accordingto claim 1 wherein the heat exchanger tank is arranged to be supportedwithin the oil storage tank such that heat is only communicated from theheating apparatus to the liquid in the storage tank through the heatexchanger fluid.
 3. The assembly according to claim 1 wherein the heatexchanger tank is arranged to be supported in sealing engagement withone of the walls of the oil storage tank.
 4. The assembly according toclaim 1 wherein the heat exchanger tank is arranged to extend generallyhorizontally inward from an upright boundary wall of the storage tank.5. The assembly according to claim 1 in combination with a productiontank arranged to receive produced hydrocarbons therein directly from awell.
 6. The assembly according to claim 1 further comprising anoverflow tank located externally of the heat exchanger tank and anoverflow passage in communication between the overflow tank and the heatexchanger tank so as to be arranged to permit expansion of the heatexchanger fluid from the heat exchanger tank into the overflow tank. 7.The assembly according to claim 1 further comprising a fluid levelmonitor arranged to monitor a level of heat exchanger fluid in the heatexchanger tank, and a controller arranged to cease operation of theheating apparatus responsive to a level of the heat exchanger fluid asmonitored by the fluid level monitor falling below a prescribed lowerlevel limit.
 8. The assembly according to claim 1 further comprising aheat exchanger temperature monitor arranged to monitor a temperature ofthe heat exchanger fluid in the heat exchanger tank, and a controllerarranged to cease operation of the heating apparatus responsive to atemperature of the heat exchanger fluid as monitored by the heatexchanger temperature monitor exceeding a prescribed upper temperaturelimit.
 9. The assembly according to claim 1 further comprising a heatexchanger temperature monitor arranged to monitor a temperature of theheat exchanger fluid in the heat exchanger tank, and a controllerarranged to actuate operation of the heating apparatus responsive to atemperature of the heat exchanger fluid as monitored by the heatexchanger temperature monitor falling below a prescribed lowertemperature limit.
 10. The assembly according to claim 1 furthercomprising a storage temperature monitor arranged to monitor atemperature of the liquid in the liquid storage tank, and a controllerarranged to cease operation of the heating apparatus responsive to atemperature of the liquid as monitored by the storage temperaturemonitor exceeding a prescribed upper temperature limit.
 11. The assemblyaccording to any one of claims 1 through 10 wherein the heat exchangertank includes a perimeter flange projecting outwardly from the boundarywalls about a circumference of the heat exchanger tank, the perimeterflange being arranged to be mounted in sealing engagement about aperimeter of an opening in the wall of the oil storage tank.
 12. Theassembly according to claim 11 wherein the perimeter flange is definedby a perimeter edge of an end wall at one end of the heat exchangertank.
 13. The assembly according to claim 11 wherein the perimeterflange includes spaced apart mounting apertures formed therein so as tobe arranged to secure the flange to the perimeter of the opening in thewall of the oil storage tank using threaded fasteners.
 14. The assemblyaccording to claim 1 wherein the heat exchanger fluid comprises heattransfer oil.
 15. The assembly according to claim 1 further comprising aproduction passage communicating through the heat exchanger tank from aninlet end of the production passage arranged to receive produced fluidfrom a well therein to outlet of the production passage arranged forcommunication with the hollow interior of the storage tank such that theproduction passage is in heat exchanging relationship with the heatingapparatus through the heat exchanger fluid.
 16. The assembly accordingto claim 15 wherein the production passage follows a sinuous paththrough the heat exchanger tank.
 17. The assembly according to claim 15wherein the production passage is above the heating assembly.
 18. Theassembly according to claim 1 wherein the heating apparatus comprises aburner tube extending through the heat exchanger tank and being arrangedto be coupled to an external burner so as to direct exhaust from theburner therethrough.
 19. The assembly according to claim 1 wherein theheating apparatus comprises an electrical resistance-type heatingelement extending through the heat exchanger tank.
 20. A method ofproducing hydrocarbons from a well comprising a wellhead, the methodcomprising: providing a storage tank in proximity to the well having aninterior storage chamber for storing produced hydrocarbons therein;providing a heating assembly comprising: a heat exchanger tank receivedwithin the interior of the storage chamber of the storage tank, the heatexchanger tank including boundary walls containing a heat exchangerfluid therein; and a heating apparatus supported within the heatexchanger tank; directing produced hydrocarbons from the well into theinterior storage chamber of the storage tank; and heating the producedhydrocarbons in the interior storage chamber of the storage tank byactuating the heating apparatus such that heat from the heatingapparatus is arranged to be communicated through the heat exchangerfluid and the boundary walls of the heat exchanger tank directly to theproduced hydrocarbons in the storage tank.